1. Field of the Invention
The present invention generally relates to the field of data access. More specifically, the invention relates to an adaptive bandwidth management system for high-performance input/output devices with variable throughput.
2. Description of the Related Art
In a computer system, an input/output (I/O) device is generally a hardware device with which the computer system may perform I/O operations. Common I/O devices include memory systems, hard drives, CD-ROM drives, and printers, among others. Such an I/O device is typically managed via a device driver, which is a software program written specifically to allow one or more applications running on the computer system to communicate with the I/O device. An application may make a request to use the I/O device via a call to the driver associated with the I/O device.
The number of I/O operations an I/O device can execute in a given time period is limited by the bandwidth of that I/O device. Since applications normally request bandwidth faster than the bandwidth can be made available, the driver maintains a queue of pending I/O requests received from the various applications running on the system. Typically, I/O requests are handled by a driver in the order in which they are received. When a queued I/O request is executed, the driver allows the application that made the I/O request to use the I/O device for a period of time. After the requested I/O operation is executed, the driver advances to the next queue position.
Some computer systems may manage I/O device bandwidth at the device driver level according to a set of rules followed by the operating system or implemented via a proprietary application programming interface (API) embedded within each application. Request scheduling for a particular I/O device is based on the bandwidth required by each application and the I/O requests currently in the queue of the driver associated with the I/O device. The maximum bandwidth required by an application may define a priority ranking of the application relative to the other applications that access the I/O device. When the queue is not empty, high priority applications are allowed to use the I/O device, regardless of queue position.
One drawback of this approach is that the bandwidth management system is prevented from making optimal scheduling decisions. For example, in a scenario where a low priority application queues I/O requests far in advance, and then a high priority application queues an I/O request only when the I/O operation is required, the I/O request of the high priority application may be delayed because the queue is clogged with low priority I/O requests. Another drawback is that when a high-bandwidth application requests more bandwidth than what is actually required to execute the relevant I/O operation, I/O device bandwidth is wasted. For example, if a high-bandwidth application uses less time to complete an I/O operation with respect to a particular I/O device than the time requested, then that I/O device remains reserved for the high-bandwidth application throughout the requested time period, even though the I/O device is not in use. Yet another drawback is that the actual bandwidth that an I/O device can handle may vary over time according to fragmentation, hardware degradation, or partial failure, among other things, thus further complicating efficient scheduling using prior art techniques.
As the foregoing illustrates, there is a need in the art for a more effective bandwidth management system.